It was a background briefing, which means that I can tell you what they said but cannot identify which official said it. Some snippets of the briefing have been reported. Most has not.

It opened with one of the agency chiefs giving a summary of the advice from the Office of National Assessments. This is the agency superimposed on the other agencies by the Fraser government. It does no spying itself, but is supposed to make sense of all the material collected by all the other agencies.

“The key judgment from the national assessment which was presented to ministers was that, notwithstanding some very significant increases in counter-terrorism capability, the threat to the West and to Australia from global Islamist terrorism is going to rise over the next five years or so, not decrease,” the official began.

“There are now more jihadists from more nationalities active in more countries than ever before. The threat picture is more diverse and less predictable.”

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The greatest threat, he said, came from Syria and Iraq. “Quite simply, they have transformed the global terrorism landscape. They have been a magnet … that no other conflict, including Afghanistan, has been.”

He estimated that up to 10,000 so-called “foreign fighters” had been drawn to the Syrian civil war and its spillover into Iraq. Why so many? One reason, he said, is that it is easy to get to: “Syria and Iraq now offer relatively easy opportunities for would-be jihadists to train and fight and kill.”

The official said that there were three types of threat . First was that the conflict zone provided “ungoverned spaces from which terrorist groups plot attacks against the West.” This was exactly the gift that Afghanistan gave al-Qaeda.

Second was the return of foreign fighters to their homelands, including Australia.

The head of another intelligence agency gave estimates of the numbers of Australians involved. This second official said that “we are looking at about 150 Australian-based individuals who are directly related in some way or other.”

Most, he said, were living in Australia “raising funds, recruiting fighters, sending supplies, proselytising, for the extremists groups in Syria”. Some had had their passports cancelled by the government on the advice of ASIO. These people still hoped to travel to Syria somehow, he said.

“And then we have got approximately 60 people that we know of currently operating in Syria or in Iraq” working with various offshoots of al-Qaeda.

They were increasingly gravitating to the most extreme of the offshoots, Islamic State in Iraq and the Levant (ISIL). This group, after declaring a caliphate, now calls itself simply Islamic State.

This second official gave some other figures: 51 or 52 Australians had had their passports cancelled to prevent them joining the conflict; about 15 Australians had died in the fighting; 14 of them had fought on the Sunni side; two young Australians had been suicide bombers; "tens" of people had returned to Australia already.

Of these, some had been disenchanted with the cause and walked away from it, but “a considerable number” had not, he said.

Australia’s experience of Afghanistan was that some 30 Australians joined the fighting there, he said. Some came home and immediately started to try making bombs. But many were inactive and did not draw attention to themselves, he said, for four or five years.

“These sort of people will require the attention of security authorities for some considerable time to come.”

Returning to the first official and his list of three types of risk to Australia, he named the third risk as “the revival of an anti-Western strain of terrorism in south-east Asia.”

Australia had suffered about 112 terrorism deaths since 2000, he said, most in Indonesia. While the Indonesian authorities had smashed Jemaah Islamiah, ISIL was exciting a new wave of Indonesians. The official cited the work of Sidney Jones, an Indonesia-based American expert on the subject.

In a January report for her think tank, the Institute for Policy Analysis of Conflict, Jones wrote: “The conflict in Syria has captured the imagination of Indonesian extremists in a way no foreign war has before.”

Several developments seem to have vindicated the intelligence agencies even in the week since the government accepted their recommendations last Monday.

On that same day, the Indonesian government of Susilo Bambang Yudhoyono announced that it was banning any support for ISIL. It warned that the group posed a threat to Indonesia’s national cohesion.

On Friday, Sydney time, the Obama administration, with utmost reluctance, decided that the US needed to return to the fight in Iraq. Obama ordered airstrikes on ISIL.

And on Monday Australians saw the photo of a young Sydney boy smiling as he held aloft the severed head of an Iraqi, his father proudly endorsing the lad: “That’s my boy!”

If there were any doubts about the seriousness of the threat posed by this obscene barbarism, they have now been dispelled.

Peter Hartcher is the international editor.

Correction. In my Saturday column, I wrote that the Immigration Minister, Scott Morrison, is frequently co-opted to join meetings of the National Security Committee of Cabinet. He is actually a full standing member.